The portion of the public network from the central office to the end user's location is called the access network, or “last mile.” The access network connects the end user to the Internet (i.e., to the backbone or core network) via the central office. To keep pace with increasing internet traffic, network operators have, in many areas, upgraded existing access networks by deploying optical fibers deeper into the last mile to shorten the lengths of copper and coaxial networks.
Among different competing optical network technologies, passive optical networks (PONs) have been one of the favored choices for these next generation access networks. With the large bandwidth of optical fibers, PONs can accommodate bandwidth-intensive voice, data, and video services. Furthermore, PONs can be built with existing protocols, such as Ethernet and ATM, which facilitates interoperability between PONs and other network equipment.
FIG. 1 illustrates an exemplary PON 100 that includes a central office 110, a single family unit (SFU) 120, and a multi-dwelling unit (MDU) 130 (i.e., a structure housing two or more residential or business units). Transmissions within PON 100 are performed between an optical line terminal (OLT), at central office 110, and optical network units (ONUs), at SFU 120 and MDU 130, over optical fibers that span the distance between them. The OLT at central office 110 couples PON 100 at its end to a metro backbone (not shown), which can be an external network belonging to, for example, an Internet service provider (ISP) or a local exchange carrier. In addition, the ONUs at SFU 120 and MDU 130 further couple PON 100 at their ends to home or business networks through customer-premises equipment (CPE) (also not shown). It is this network structure that allows end user devices coupled to home or business networks within SFU 120 and MDU 130 to send data to and receive data from the metro backbone over PON 100.
The portion of PON 100 closest to central office 110 is commonly referred to as the feeder area 150. This area includes one or more feeder cables that each has multiple fibers. Passive optical splitters/combiners 140 are used to split the individual fibers of the feeder cables into multiple distribution fibers that fall within the second portion of PON 100, which is commonly referred to as the distribution area 160. The distribution fibers are then further split by additional passive optical splitters/combiners 140 into multiple drop fibers that extend to SFU 120 and MDU 130. The drop fibers fall within the third and final portion of PON 100, which is commonly referred to as the drop area 170.
In general, signals sent downstream over these three portions of PON 100, by the OLT at central office 110, are split by passive optical splitters/combiners 140 and are received by the ONUs at SFU 120 and MDU 130. Conversely, signals sent upstream over these three portions of PON 100, by the ONUs at SFU 120 and MDU 130, are combined by passive optical splitters/combiners 140 and are received by the OLT at central office 110. To avoid collisions in the upstream direction and to share the fiber-channel capacity fairly, the OLT at central office 110 and the ONUs at SFU 120 and MDU 130 implement some form of arbitration.
It should be noted that PON 100 illustrates only one exemplary fiber distribution topology (i.e., a tree topology) and that other point-to-multipoint fiber distribution topologies, such as ring and mesh topologies, are possible.
In prior access networks, distribution area 160 and/or drop area 170 were deployed using copper and coaxial cables. By extending fiber cables deeper into the access network, all the way to the home and building, PON 100 can accommodate bandwidth-intensive voice, data, and video services that these prior access networks could not handle. In general, the only remaining portion of the network between central office 110 and an end user's device at SFU 120 and MDU 130 that potentially is not optically connected, is within the local area networks at these locations (i.e., within metallic area 180). However, over such short copper and/or coaxial wiring distances, current local area network technology generally provides adequate bandwidth.
Although PON 100 improves the performance of the last mile, the number of drop fibers available within drop area 170 cannot easily be increased without potentially adding additional feeder and distribution cables, which can be an expensive undertaking. This is a direct result of the passive nature of PON 100 which uses passive devices (i.e., passive optical splitters/combiners 140) that do not require power to split optical signal power from one fiber into several fibers. Typically, a single fiber from the OLT at central office 110 is limited to being split into 32 different drop fibers (although 64, 128, and even higher splits are possible). Therefore, drop fibers are a fairly valuable commodity.
For SFUs, such as SFU 120, there is generally no way around running a dedicated drop fiber to the boundary of the home to be used by a single end user or end user family. However, in MDUs, such as MDU 130, which includes two or more residences or businesses, there exists a potential to share a single drop fiber among multiple residences and/or businesses and their respective end users.
Current implementations of ONUs for MDUs, such as MDU 130, either provide a scalable solution (i.e., one which allows a growing number of end users to share a single drop fiber) at a high initial cost, or a non-scalable solution (i.e., one which only allows a fixed number of end users to share a single drop fiber) at a relatively low initial cost. In addition, the conventional scalable solutions typically have high associated maintenance costs due to their architectures.
Therefore, what is needed is a scalable ONU solution for an MDU that has a low initial cost (or first port cost) and low associated maintenance costs.
The present invention will be described with reference to the accompanying drawings. The drawing in which an element first appears is typically indicated by the leftmost digit(s) in the corresponding reference number.